German Patent 19 30 952 discloses a temperature-sensitive element adapted for use as a motor protection sensor. A thermistor is mounted in a window of a flexible insulating board. Both sides of the thermistor are covered by thin insulating sheets which support printed leads for making contact with the thermistor. The temperature sensitive element, together with the insulating sheets, are located in a leaf-like envelope or shrouding, the ends of the conductive leads being connected to terminal ends of a signal transmission line by means of solder contacts.
This prior art device is, due to its flattened structure, practically usable only in coils of an electrical machine, and cannot be installed in protective tubes.
Further, East German Patent DD-PS 81,231 discloses a resistance thermometer for temperature measurement under conditions of extreme fluctuation, such as in the exhaust gases of ship diesel machinery. A thermometer has a protective tube, including an insulating tube made from a suitable ceramic material for receiving one or multiple measuring resistors including inner conductors. These conductors are in turn surrounded by insulating tubes of a suitable ceramic material. The inner conductors must either be made in one piece running from the measuring resistance coils to the contacts in the terminal head, or one must provide a connecting point in the inner conductor which lies outside the critical oscillation or fluctuation zone. The insulating tube combination is closed off at its transition to the terminal head by a heat-tolerating, hardened, but not embrittled, paste.
Experience has shown that making the connection between the thermal sensor and the conducting leads at separate connection points represents a substantial problem in terms of vulnerability to oscillation.
U.S. Pat. No. 2,916,537, REID & GROSS/GENERAL DYNAMICS discloses a temperature sensor which, for reasons of higher sensitivity and lower weight, is made in the form of conductive tracks on a board-like plastic carrier, such as epoxy resin (col. 3, line 53). The ends of the tracks which form the thermocouple element are each provided with a respective connection contact for lead wires. The temperature measurement is done in a flowing medium which is fed through openings in the board forming the substrate. Such an arrangement is suitable for measurement of a medium which flows over a large flat surface, but its use in a protective tube is impractical because of the large surface area required.
Accordingly, it is an object of the present invention to provide a temperature sensor construction in which the temperature sensor is located in a protective tube and in which conductors running through the tube have connection contacts to signal transmission conductors, yet in which the measuring element is practically oscillation-free. In particular, the use of economical elements should reduce resonance phenomena resulting from audio-frequency machine vibrations and which until now tended to cause destruction of conductors and/or erroneous measurement results. The field of use particularly includes audio-frequency engine vibrations from compressors, from diesel drive mechanisms and exhaust gas temperature measurement in internal combustion engines. Depending upon the application, one should be able to use, as the temperature sensor, either temperature measuring resistors or piezo-electric temperature sensors.